Fred Miller (Tony Randall) must prove that his new design for an underwater home is viable by convincing his family to live in it for 30 days. His son and daughter (Gary Tigerman and Kay Cole) are members of an emerging pop rock band (Richard Dreyfuss and Lou Wagner) whom they invite to live with them during the experiment. Their temporary home, which Miller dubs the “Green Onion,” is 90 feet below the surface of the ocean and is filled with super-modern appliances and amenities for house-wife Vivian (Janet Leigh), all designed by Miller. A hole in the floor provides direct access to and from the sea.
The group are soon joined by a live-in seal named Gladys and a pair of dolphins (Duke and Duchess), which stay close at hand and fend off unwanted sharks. They are confronted by many obstacles including a rival designer (Ken Berry) from Undersea Development, Inc. who begins to cause problems.
Meanwhile, the band’s single has gotten the attention of record executive Nate Ashbury (Roddy McDowall), who decides to sign them sight-unseen. He takes the liberty of booking them for an important television performance on The Merv Griffin Show without first communicating with them. After learning that they are inaccessible under the sea, he proves that the show must go on and that he will go to great lengths to reach them. They get their airing on television, but the U.S. Navy is put on alert by the sounds of music coming from the sea. A naval fleet is dispatched to investigate what must surely be a Communist plot!